A long-lasting and stable liquid calcium indicator

Abstract

The present application relates to the technical field of metal content determination, and specifically discloses a long-lasting and stable liquid calcium indicator, comprising an indicator component A and a dilution component B; the indicator component A is obtained by compounding calcein, phenol red, and thymolphthalein; the dilution component B is a glycerol-triethanolamine mixture; the liquid calcium indicator is obtained by adding 1g of calcein, 0.15g of phenol red, and 1g of thymolphthalein to a 100mL glycerol-triethanolamine mixture; the liquid calcium indicator of the present application significantly extends the storage period compared to a solid calcium indicator; the newly prepared liquid calcium indicator can be stored at room temperature for 63 days without deterioration and can accurately indicate the titration endpoint; in addition, the amount of the liquid calcium indicator added can be accurately controlled, specifically by using a pipette, while the solid calcium indicator cannot be accurately controlled.

Description

Technical Field

[0001] The present application relates to the technical field of metal content determination, and more particularly, to a long-lasting and stable liquid calcium indicator. Background Art

[0002] Dispersions of limestone (CaCO3) or slaked lime (Ca(OH)2) are often used as flue gas absorbents. Flue gas generated during production is directly and continuously passed through the absorbent, or the absorbent is sprayed directly into the flue gas. This causes the limestone or slaked lime to react chemically with toxic and harmful gases such as NO, NO2, Cl2, HF, F2, SO2, and SO3 in the flue gas to produce calcium-containing compounds such as Ca(NO2)2, Ca(NO3)2, CaCl2, CaF2, CaSO3, and CaSO4, thereby removing toxic and harmful gases from the flue gas. As the reaction between the limestone or slaked lime and toxic and harmful gases such as NO, NO2, Cl2, HF, F2, SO2, and SO3 in the flue gas proceeds, the effective calcium content in the limestone or slaked lime dispersion decreases. To ensure effective flue gas treatment, testing the effective calcium content in the limestone or slaked lime dispersion is often necessary during actual treatment.

[0003] Currently, the main analytical methods for measuring calcium content include disodium ethylenediaminetetraacetic acid (EDTA) titration, potassium permanganate, tribromoarsenazo dual-wavelength spectrophotometry, atomic absorption spectroscopy, potentiometric titration, and inductively coupled plasma atomic emission spectrometry. EDTA titration is the most widely applicable and common method, offering advantages such as a wide range of calcium concentrations (contents) (0.1%-99.90%), ease of operation, high reliability of analytical results, and minimal consumables. When using EDTA titration to determine the calcium content of limestone or slaked lime, an indicator is typically added to the sample solution.

[0004] When measuring calcium using disodium ethylenediaminetetraacetic acid (EDTA) titration, two commonly used indicators are calcium indicator and calcein. Calcium indicator, also known as calcium red or NN indicator, is a black powder commonly used to determine calcium ion content. At a pH of 12-14, the calcium indicator appears blue and forms a wine-red complex with calcium ions. The difference in color between the two indicates the endpoint of the titration. However, during titration, the concentration of other ions that may affect / interfere with detection accuracy must be low. If the concentration of other ions in the test solution that may affect / interfere with detection accuracy exceeds the allowable concentration, these ions must be removed from the test solution before titration, a complex and time-consuming process. Calcein can generate a yellow-green fluorescent complex with calcium ions in water. When pH>13, the calcium in the test solution is titrated with EDTA titration. The complexing ability of EDTA and calcein is greater than the complexing ability of calcium and calcein. Therefore, EDTA will continuously capture the calcein in the fluorescent yellow-green complex. When EDTA completely captures the calcein in the fluorescent yellow-green complex, the yellow-green fluorescence in the test solution disappears and the test solution turns brown-red, indicating that the titration endpoint has been reached. The concentration of other ions that calcein allows to affect / interfere with the detection accuracy is higher than the concentration allowed by the calcium indicator. In the related art, since the aqueous solution of calcium indicator and calcein is unstable, it is often mixed with potassium nitrate (or potassium sulfate, sodium chloride, potassium chloride, etc.) in a certain ratio to form a solid calcium indicator for use in analytical experiments. However, it is found in actual application that solid potassium nitrate powder (including powders such as potassium sulfate, sodium chloride, potassium chloride) has extremely strong water absorption and air absorption, which makes the solid calcium indicator very easy to absorb substances such as acidic gases, acidic water, oxygen and some organic gases in the air. The above substances react directly with the indicator components (calcein, phenol red, thymolphthalein) adsorbed on the surface of the solid potassium nitrate powder, which not only affects the judgment of the titration end point color, but also causes the generation of problems such as the titration end point hysteresis or early titration end point; Moreover, the storage period of the newly configured solid calcium indicator is relatively short, and it will generally become ineffective after being placed for 2-3 weeks at room temperature; In addition, because the mass of the solid calcium indicator added is very small, the amount of solid calcium indicator added cannot be accurately controlled, and the mass added cannot be kept equal due to uncontrollable human factors, and the uncertainty of the indicator dosage will cause the end point color to be different in depth, making it difficult to grasp the judgment of the titration end point, and the generated complex is unstable, and the accuracy and precision of the test results are not high. Based on the above statements, the present application provides a long-lasting and stable liquid calcium indicator. Summary of the Invention

[0005] In order to solve the problems in the related art, such as the short storage period of solid calcium indicators, the difficulty in quantitative dosage, the insensitive end point color change, and the low accuracy of detection results, the present application provides a long-lasting and stable liquid calcium indicator.

[0006] The present application provides a long-lasting and stable liquid calcium indicator, which adopts the following technical solution:

[0007] A long-acting and stable liquid calcium indicator comprises an indicator component A and a dilution component B; the indicator component A is prepared by compounding calcein, phenol red and thymolphthalein; and the dilution component B is a glycerol-triethanolamine mixed solution.

[0008] By adopting the above technical solution, the diluent in the liquid calcium indicator of the present application is a glycerol-triethanolamine mixture, wherein concentrated glycerol (glycerol) and the aqueous solution are neutral, and concentrated triethanolamine and the aqueous solution are medium-weakly alkaline. Both glycerol and triethanolamine can absorb substances such as acidic gases, some organic gases, oxygen, and acidic water in the air. Substances such as acidic gases, some organic gases, oxygen, and acidic water in the detection room air are absorbed and diluted by the glycerol and triethanolamine in the liquid calcium indicator, making the concentration of the above substances in the liquid calcium indicator very low, and thus cannot react with the indicator component A (calcein, phenol red, and thymolphthalein) in the liquid calcium indicator or react slowly.

[0009] Preferably, the mass ratio of calcein, phenol red and thymolphthalein is 1:0.15:1.

[0010] Preferably, the glycerol-triethanolamine mixed solution is obtained by compounding 95% by volume of glycerol and 5% by volume of triethanolamine.

[0011] Preferably, the mass concentrations of glycerol and triethanolamine are both 98 wt%.

[0012] By adopting the above technical solution, the use of triethanolamine in the liquid calcium indicator is intended to prevent acidic gases, acidic moisture, and oxygen from reacting with the indicator component A (calcein, phenol red, and thymolphthalein) in the liquid calcium indicator. The presence of a small amount of triethanolamine in the liquid calcium indicator makes the liquid calcium indicator weakly alkaline. When in contact with acidic gases, acidic moisture, some organic gases, oxygen, etc. in the air, the triethanolamine in the liquid calcium indicator can undergo a neutralization reaction with the acidic gases and acidic moisture, thereby preventing the acidic gases, acidic moisture, and oxygen from reacting with the indicator component A (calcein, phenol red, and thymolphthalein) in the liquid calcium indicator, thereby preventing the indicator component A (calcein, phenol red, and thymolphthalein) from rapidly generating other substances and becoming ineffective.

[0013] However, the higher the triethanolamine content in the liquid calcium indicator, the better. This is because the higher the triethanolamine content, the stronger the alkalinity of the liquid calcium indicator, from weak alkalinity to medium-strong alkalinity. The properties of the indicator component A (calcein, phenol red and thymolphthalein) will change over time under medium-strong alkalinity, and it will not be able to be preserved for a long time, which will affect the accuracy and precision of the test value. The applicant has found that when the triethanolamine content in the glycerol-triethanolamine mixture is 5% by volume, the liquid calcium indicator can be stored for the longest time. It can maintain its properties unchanged for 63 days at room temperature. During this period, it does not need to be re-prepared and does not affect the accuracy and precision of the test value.

[0014] Preferably, the liquid calcium indicator is prepared by adding 1 g of calcein, 0.15 g of phenol red and 1 g of thymolphthalein to 100 mL of a glycerol-triethanolamine mixture.

[0015] By adopting the above technical scheme, the present application adopts a glycerol-triethanolamine mixture of calcein, phenol red and thymolphthalein as a liquid calcium indicator, which can effectively ensure that the color change at the titration endpoint of the calcium-containing solution to be measured is sharp, the color chromaticity of the calcium-containing solution to be measured remains consistent, and the color change at the titration endpoint can be quickly and simply judged, and the operation is simple. The present application can effectively avoid the problem that the color change of the calcium indicator in the calcium-containing solution to be measured is not sharp at the titration endpoint; or when the operator adds the calcium indicator to the calcium-containing solution to be measured, the mass added cannot be kept equal due to uncontrollable human factors, resulting in the color chromaticity in the calcium-containing solution to be measured being of different shades, making it difficult to accurately judge the titration endpoint and increasing the titration error (end point error), thereby improving the detection accuracy and precision. Compared with a calcium indicator using solid potassium nitrate as a diluent, the method of the present application is less likely to deteriorate at room temperature, has a longer effective use time, is more convenient to use, and is simpler to operate. The color change of the calcium-containing solution to be tested near the titration endpoint is more acute, making it easier to accurately determine the titration endpoint, and the detection precision and accuracy are higher.

[0016] In summary, this application has the following beneficial effects:

[0017] The present invention discloses a liquid calcium indicator using a glycerol-triethanolamine mixture as a diluent. The presence of a small amount of triethanolamine renders the liquid calcium indicator weakly alkaline, which can neutralize acidic gases and acidic water in the liquid calcium indicator over a long period of time, maintaining the liquid calcium indicator weakly alkaline or neutral for a long period of time. The glycerol-triethanolamine mixture can also prevent or slow the reaction of oxygen and water with the indicator component. The applicant has discovered that using a 95% by volume glycerol (glycerin) and 5% by volume triethanolamine diluent in the liquid calcium indicator allows the liquid calcium indicator to be stored for a long period of time (at least 63 days) without changing its properties, without affecting the accuracy and precision of the test value.

[0018] The liquid calcium indicator of the present application significantly extends the storage period compared to a solid calcium indicator. A newly prepared liquid calcium indicator can be stored at room temperature for 63 days without deterioration and can accurately indicate the titration endpoint. In addition, the amount of the liquid calcium indicator added can be accurately controlled, specifically by using a pipette, while this cannot be accurately controlled with a solid calcium indicator. DETAILED DESCRIPTION

[0019] The present application is further described in detail below with reference to the embodiments.

[0020] Example

[0021] Example 1

[0022] A long-lasting and stable liquid calcium indicator comprises an indicator component A and a dilution component B; wherein the indicator component A is prepared by compounding calcein, phenol red, and thymolphthalein, and the mass ratio of calcein, phenol red, and thymolphthalein is 1:0.15:1;

[0023] The dilution component B is a glycerol-triethanolamine mixture, specifically a mixture of 95% by volume of glycerol and 5% by volume of triethanolamine, with the mass concentrations of glycerol and triethanolamine both being 98wt%;

[0024] The liquid calcium indicator is prepared by mixing 1 g of calcein, 0.15 g of phenol red, and 1 g of thymolphthalein with 100 mL of a glycerol-triethanolamine mixture.

[0025] Preparation method of liquid calcium indicator: (1) Add 95 ml of glycerol and 5 ml of triethanolamine into a glass beaker and stir evenly to obtain a glycerol-triethanolamine mixture; (2) Add 1 g of calcein, 0.15 g of phenol red and 1 g of thymolphthalein into the glass beaker containing the glycerol-triethanolamine mixture, then place the glass beaker into an ultrasonic oscillator and oscillate with ultrasound until the calcein, phenol red and thymolphthalein are completely dissolved, thereby obtaining the prepared liquid calcium indicator.

[0026] Comparative Example

[0027] Comparative Example 1

[0028] Preparation method of national standard solid calcium indicator: Place 1g of calcein, 0.15g of phenolphthalein, 1g of methylthymol blue, and 100g of potassium nitrate (analytical purity) into an agate mortar, and grind them manually with an agate mortar handle to a fine powder to obtain the national standard solid calcium indicator.

[0029] Comparative Example 2

[0030] The solid calcium indicator of the present application comprises an indicator component A and a dilution component C; wherein the indicator component A is obtained by compounding calcein, phenol red and thymolphthalein, and the mass ratio of calcein, phenol red and thymolphthalein is 1:0.15:1; the dilution component C is solid potassium nitrate powder;

[0031] The solid calcium indicator of the present application is prepared by adding 1 g of calcein, 0.15 g of phenol red and 1 g of thymolphthalein to 100 g of solid potassium nitrate powder and mixing them.

[0032] The solid calcium indicator of the present application is prepared by placing 1 g of calcein, 0.15 g of phenol red, 1 g of thymolphthalein, and 100 g of potassium nitrate (analytical purity) into an agate mortar and manually grinding them into a fine powder using an agate mortar handle to obtain the solid calcium indicator of the present application.

[0033] 1. Using the national limestone component analysis standard material (GBW03106), the calcium oxide standard value is 51.61%. According to the GB / T5762-2012 detection method, a control test of the liquid calcium indicator of Example 1 of the present application and the national standard solid calcium indicator of Comparative Example 1 was carried out.

[0034] 1. On the 7th day after preparation, the accuracy and precision of the two calcium indicators in detecting calcium-containing standard substances were compared. The results are shown in Table 1.

[0035] Table 1:

[0036]

[0037] 2. On the 21st day after preparation, the accuracy and precision of the two calcium indicators in detecting calcium-containing standard substances were compared. The results are shown in Table 2.

[0038] Table 2:

[0039]

[0040]

[0041] From the data in Tables 1 and 2, it can be seen that the detection time is 7 days and 21 days after the preparation of the two calcium indicators, respectively; the national limestone component analysis standard material (GBW03106) was tested and a control experiment was conducted to test the accuracy and precision of the average measurement values ​​of the two calcium indicators on the 7th and 21st days after preparation and the standard value (GBW03106).

[0042] From the first control experiment on the 7th day, we can see that:

[0043] (1) The difference between the average value and the standard value (absolute error) is small. The difference between the liquid calcium indicator of the present application is only 0.038%, and the national standard solid calcium indicator is only 0.043%. The difference between the average value and the standard value (absolute error) of the two calcium indicators is very small, only 0.005%.

[0044] (2) The relative error (accuracy) of the average measured value is small. The relative error (accuracy) of the liquid calcium indicator of the present application is only 0.074%, while that of the national standard solid calcium indicator is only 0.083%. The difference in the relative error (accuracy) of the two calcium indicators is very small, only 0.009%.

[0045] (3) The standard deviation (precision) of the average measured value is small. The standard deviation of the liquid calcium indicator of the present application is only 0.053%, while that of the national standard solid calcium indicator is only 0.058%. The difference in the standard deviation (precision) of the two calcium indicators is very small, only 0.005%.

[0046] From the second control experiment on the 21st day, we can see that:

[0047] (1) The difference (absolute error) between the average value and the standard value of the national standard solid calcium indicator is large, while the difference (absolute error) between the average value and the standard value of the liquid calcium indicator of the present application is small. The liquid calcium indicator of the present application is 0.043%, which is very close to the difference of 0.038% in the first control experiment on the 7th day, only 0.005%, which is 13% higher; while the national standard solid calcium indicator is 0.155%, which is 0.112% different from the difference of 0.043% in the first control experiment on the 7th day, which is 260% higher; the difference (absolute error) between the average value and the standard value of the two calcium indicators is also large, which is 0.112%.

[0048] (2) The relative error (accuracy) of the average measured value of the national standard solid calcium indicator is large, while the difference (absolute error) between the average value and the standard value of the liquid calcium indicator of the present application is small. The relative error of the liquid calcium indicator of the present application is 0.083%, which is very close to the difference of 0.074% in the first control experiment on the 7th day, only 0.009%, which is 12% higher; while the relative error (accuracy) of the national standard solid calcium indicator is 0.30%, which is 0.217% lower than the difference of 0.083% in the first control experiment on the 7th day, which is 261% higher; the difference in the relative error (accuracy) of the two calcium indicators is also large, which is 0.217%.

[0049] (3) The standard deviation (precision) of the average measurement value of the national standard solid calcium indicator is large, while the difference (absolute error) between the average value and the standard value of the liquid calcium indicator of the present application is small. The standard deviation of the liquid calcium indicator of the present application is 0.056%, which is very close to the difference of 0.053% in the first control experiment on the 7th day, only 0.003%, and is 5.7% higher; while the standard deviation of the national standard solid calcium indicator is 0.18%, which is 0.122% different from the difference of 0.058% in the first control experiment on the 7th day, and is 210% higher; the difference in the standard deviation (precision) of the two calcium indicators is also large, which is 0.124%.

[0050] In summary:

[0051] (1) The second control experiment of the liquid calcium indicator of the present application was conducted on the 21st day after preparation, and was compared with the first control experiment conducted on the 7th day after preparation. The difference (absolute error) and relative error (accuracy) between the average measured value and the standard value, as well as the standard deviation (precision) were very small, only 13%, 12%, and 5.7% higher, respectively. This shows that the prepared liquid calcium indicator of the present application can be stored for a long time at room temperature, and its properties remain unchanged within 21 days, without affecting the accuracy and precision of the test value.

[0052] (2) The second control experiment conducted on the 21st day after the national standard solid calcium indicator was prepared was compared with the first control experiment conducted on the 7th day after the preparation. The difference (absolute error) and relative error (accuracy) between the average measured value and the standard value, as well as the standard deviation (precision) were very different, which were 260%, 261% and 210% higher respectively. This shows that the prepared national standard solid calcium indicator cannot be stored for a long time. Its properties will change after 21 days, and the accuracy and precision of the test value will decrease significantly, affecting the accuracy and precision of the test value.

[0053] 3. Comparison of the accuracy and precision of two calcium indicators in detecting calcium-containing standard substances at different preparation days. The results are shown in Table 3.

[0054] Table 3:

[0055]

[0056] Note: The average value in Table 3 is the average value of 6 measurements.

[0057] As shown in Table 3, the liquid calcium indicator of the present application can maintain its properties unchanged for 63 days without affecting the accuracy and precision of the test value and without requiring re-preparation. In contrast, the national standard solid calcium indicator can only maintain its properties unchanged for 21 days without affecting the accuracy and precision of the test value and without requiring re-preparation, which is 42 days shorter than the 63-day storage time of the liquid calcium indicator of the present application.

[0058] 2. Using the national limestone component analysis standard material (GBW03106), the calcium oxide standard value is 51.61%. According to the GB / T5762-2012 detection method, a control test of the national standard solid calcium indicator of comparative example 1 of this application and the solid calcium indicator of this application of comparative example 2 was carried out.

[0059] 1. Comparison of the accuracy and precision of two solid calcium indicators in detecting calcium-containing standard substances at different preparation days. The results are shown in Table 4.

[0060] Table 4:

[0061]

[0062] Note: The average value in Table 4 is the average of 6 measurements.

[0063] As can be seen from the data in Table 4, the two solid calcium indicators can only maintain their properties unchanged within 21 days, without affecting the accuracy and precision of the test values, and do not need to be re-prepared. This is 42 days shorter than the storage time of 63 days for the liquid calcium indicator. This shows that the prepared national standard solid calcium indicator, like the solid calcium indicator of the present application, cannot be stored for a long time. After 21 days, the properties will change, and the accuracy and precision of the test values ​​will significantly decrease, affecting the accuracy and precision of the test values.

[0064] The difference between the average measured value and the standard value (absolute error) and the relative error (accuracy) as well as the absolute error and relative error of the standard deviation (precision) are very small. The absolute errors are: 0.002%, 0.004%, 0.002% on the 7th day; 0.001%, 0.002%, 0.001% on the 14th day; 0.002%, 0.004%, 0.002% on the 21st day; the relative errors are: 4.76%, 4.94%, 3.51% on the 7th day; 1.23%, 1.27%, 0.99% on the 14th day; 1.30%, 1.34%, 1.12% on the 21st day, indicating that there is no significant difference between the two solid calcium indicators.

[0065] 2. Compare the t values ​​of the significant difference test of the two solid calcium indicators on the 7th, 14th and 21st days of preparation respectively.

[0066] When the confidence level P = 95% and the degree of freedom f = 6, calculate t 国标 With t 本申请 The obtained data are shown in Table 5.

[0067] t af The value is the t value stipulated by the state when the confidence level P = 95% and the degree of freedom f = 6. 国标 With t 本申请 Greater than t af When the value is t, there is a significant difference, indicating that these two solid calcium indicators cannot be used to indicate the titration end point. 国标 With t 本申请 Less than t af When the values ​​are equal, there is no significant difference, which means that these two solid calcium indicators can be used to indicate the titration end point.

[0068] Table 5:

[0069] Preparation time 7 days 14 days 21 days t national standard 1.64 1.82 1.92 This application 1.66 1.81 1.92 taf value 2.57 2.57 2.57

[0070] From the data in Table 5, we can see that after the significant difference test of the two solid calcium indicators on the 7th, 14th and 21st days of preparation, the calculated t 国标 With t 本申请 The data is much lower than t af The data showed that there was no significant difference, indicating that the two solid calcium indicators could be used to indicate the titration endpoint. Moreover, the t values ​​of the two solid calcium indicators were significantly different on the 7th, 14th, and 21st days of preparation. 国标 With t 本申请 The data differences were 0.02, 0.01, and 0.00, respectively, indicating a significant difference between the two solid calcium indicators (t 国标 With t 本申请 ) is extremely small and much smaller than t af value.

[0071] 3. With other factors unchanged, only the volume contents of glycerol and triethanolamine in Example 1 were changed, and the storage period of the resulting liquid calcium indicator was tested. The results are shown in Table 6.

[0072] Table 6:

[0073] Triethanolamine volume content / % 0 2.5 5 7.5 10 12.5 Glycerol volume content / % 100 97.5 95 92.5 90 87.5 Liquid calcium indicator storage period 35 days 49 days 63 days 49 days 35 days 21 days

[0074] The data in Table 6 show that when the triethanolamine content in the glycerol-triethanolamine mixture is 5% by volume, the liquid calcium indicator can be stored the longest, and its properties remain unchanged for 63 days without affecting the accuracy and precision of the test value, and no re-preparation is required.

[0075] The specific embodiments are merely explanations of the present application and are not limitations of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the embodiments as needed, but as long as they are within the scope of the claims of the present application, they are protected by patent law.

Claims

1. A long-lasting and stable liquid calcium indicator, characterized in that: The liquid calcium indicator includes an indicator component A and a dilution component B; the indicator component A is obtained by compounding calcein, phenol red and thymolphthalein; the dilution component B is a glycerol-triethanolamine mixture; the glycerol-triethanolamine mixture is obtained by compounding 95% by volume of glycerol and 5% by volume of triethanolamine; the mass concentrations of the glycerol and triethanolamine are both 98wt%.

2. The long-lasting and stable liquid calcium indicator according to claim 1, characterized in that The mass ratio of the calcein, phenol red and thymolphthalein is 1:0.15:

1.

3. The long-acting and stable liquid calcium indicator according to claim 1 or 2, characterized in that The liquid calcium indicator is prepared by adding 1 g of calcein, 0.15 g of phenol red, and 1 g of thymolphthalein into a 100 mL glycerol-triethanolamine mixture.

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